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Abstract The description of the cloud vertical structure remains the key source of uncertainty in climate studies. Based on the CloudSat dataset, the differences in cloud vertical structures between the active and break spells of the East Asian summer monsoon are analyzed by using the composite analysis method. During the active spell, more clouds appear, the occurrence frequency of single-layer clouds significantly decreases, and the occurrence frequency of clouds with two and more layers obviously increases. The lowest layer of the cloud is thicker than the higher layer during the active spell, while the highest layer of the cloud is thicker than the lower layer during the break spell. The clouds in the southern region of the study area are thicker than the clouds in the northern region during the active spell and thinner than the clouds in the northern region during the break spell. From the active spell to the break spell, the clouds became sparser in the southern region but more compact in the northern region. During the active spell, the cloudiness anomaly demonstrates an obvious northward-tilting structure from the upper atmosphere to the lower atmosphere because the large value center of high clouds is located in the south of the study area, while the middle and low-level clouds are located in the center of the study area. Both convective precipitation and stratiform precipitation occur in the southern region during the active spell, while the northern region is mainly dominated by convective precipitation. The cloud ice water content increases during the active spell and decreases during the break spell. During the active spell, the cloud liquid water content (LWC) increases in most of the study area, and the positive LWC anomaly exhibits an apparent northward-tilting structure from the upper level to the lower level. During the break spell, the LWC decreases in the northern region, and the negative anomaly tilts northward from the upper level to the lower level. However, the shallow convective clouds in the southern region are not completely suppressed during the break spell, and abundant positive LWC anomalies are observed in the lower troposphere. Highlights • An obvious vertical northward-tilting structure of cloud is found during the active spell. • From active to break spell, the clouds became sparser in the south but more compact in the north of East Asia. • The shallow convective clouds in the southern area are not completely suppressed during the break spell. [ABSTRACT FROM AUTHOR]

Tropical cyclone's activities can affect the ozone pollution characteristics to a certain extent over the Pearl River Delta (PRD) region based on different track types of tropical cyclones. In this study, we utilize the Finite Mixture Model algorithm to classify tropical cyclones which land on the South China coastal area between 2009 and 2018 into 6 track's types, and those types are land on the PRD region directly (A1 type), the east of the PRD region (B1 and B2 types) and the west of the PRD region (C1, C2 and C3 types) respectively. Combined with observation data, the results indicate that the A1 type, B1 type and B2 type tropical cyclones can increase the ozone concentration about 44.9% ∼ 65.3% in the PRD region before landfall accompanied with stagnant meteorological conditions usually, such as high temperature (>27 °C), low humidity (<80%) or weak wind (<3 m/s). And it should be emphasized that, due to the northward or northeastward deflection of the tracks, the ozone concentration in the PRD region does not decrease obviously (<10%) on the landing-day under B1 and B2 types, and ozone pollution maybe persistent longer than other types. By simulating typical cases of each track's type within WRF-Chem model coupled with process analysis method, and the results indicate that tropical cyclone's peripheral subsidence airflow is more obvious over the PRD region under A1, B1 and B2 cases before landfall, and it maybe an external condition which can limit the development of boundary layer and vertical diffusion of ozone, rather than transporting ozone downward from the upper atmosphere to the near surface level. In addition, based on process analysis result, the chemical reaction with strong radiation condition maybe the essential cause of ozone production and pollution, and the physical process can cause the ozone consumption. • Quantifying the influence of tropical cyclones tracks on ozone pollution. • northward deflection could lead to persistent pollution. • Strong radiation before landing is the essential cause of ozone production. [ABSTRACT FROM AUTHOR]

Planetary boundary layer (PBL) height characteristics over the Indian sub-continent at diurnal to seasonal scales and its controlling factors in relation to monsoon are investigated. The reanalysis (Modern Era Retrospective analysis for Research and Applications, MERRA) PBL heights (PBLH) used for the study are validated against those derived from radiosonde observations and radio occultation air temperature and humidity profiles. The radiosonde observations include routine India Meteorological Department observations at two locations (coastal and an inland) for one full year and campaign based early afternoon radiosonde observations at six inland locations over the study region for selected days from May–September 2011. The temperature and humidity profiles from radio occultations spread over the sub-continent at irregular timings during the year 2011. The correlations and root mean square errors are in the range 0.74–0.83 and 407 m–643 m, respectively. Large pre-monsoon, monsoon and post-monsoon variations in PBL maximum height (1000 m–4000 m), time of occurrence of maximum height (11:00 LST–17:00 LST) and growth rate (100 to 400 m h − 1 ) are noted over the land, depending on geographical location and more significantly on the moisture availability which influences the surface sensible and latent heat fluxes. The PBLH variations associated with active-break intra-seasonal monsoon oscillations are up to 1000 m over central Indian locations. Inter relationship between the PBLH and the controlling factors, i.e. Evaporative Fraction, net radiation, friction velocity, surface Richardson number, and scalar diffusivity fraction, show significant variation between dry and wet PBL regimes, which also varies with geographical location. Evaporative fraction has dominant influence on the PBLH over the region. Enhanced entrainment during monsoon contributes to reduction in PBLH, whereas the opposite effect is noted during dry period. Linear regression, cross wavelet and Analysis of Variance (ANOVA) methods are used to elucidate the role of controlling factors and interactions on PBLH in relation to monsoon. [ABSTRACT FROM AUTHOR]

To investigate changes in the ozone (O 3) chemical production regime over the contiguous United States (CONUS) with accurate knowledge of concentrations of its precursors, we applied an inverse modeling technique with Ozone Monitoring Instrument (OMI) tropospheric nitrogen dioxide (NO 2) and total formaldehyde (HCHO) retrieval products in the summers of 2011, 2014, and 2017, years in which United States National Emission Inventory were based. The inclusion of dynamic chemical lateral boundary conditions and lightning-induced nitric oxide emissions significantly account for the contribution of background sources in the free troposphere. Satellite-constrained nitrogen oxide (NO x) and non-methane volatile organic compounds (NMVOCs) emissions mitigate the discrepancy between satellite and modeled columns: the inversion suggested 2.33–2.84 (1.07–1.34) times higher NO x over the CONUS (over urban regions) and 0.28–0.81 times fewer NMVOCs emissions over the southeastern United States. The model-derived HCHO/NO 2 column ratio shows gradual spatial changes in the O 3 production regime near urban cores relative to previously defined threshold values representing NO x and VOC sensitive conditions. We also found apparent shifts from the NO x -saturated regime to the transition regime (or the transition regime to the NO x -limited regime) over the major cities in the western United States. In contrast, rural areas, especially in the east-southeastern United States, exhibit a decreased HCHO/NO 2 column ratio by −1.30 ± 1.71 with a reduction in HCHO column primarily driven by meteorology, becoming sensitive to VOC emissions. Results show that incorporating satellite observations into numerical modeling could help policymakers implement appropriate emission control policies for O 3 pollution. • Top-down estimated NO x and NMVOCs emissions enable us to have accurate knowledge of the ozone chemical regime. • The dynamic lateral boundary conditions and lightning-induced emission improve the model performance in the upper atmosphere. • Many urban regions have shifted to NOx-limited condition, while the southeastern U.S. becomes sensitive to VOC emissions. [ABSTRACT FROM AUTHOR]

Abstract: Research on regional and global lightning activity and the global electrical circuit is summarized. This area of activity has greatly expanded through observations of lightning by satellite and through increased use of the natural (Schumann) resonances of the Earth–ionosphere cavity. The global electrical circuit provides a natural framework for monitoring global change on many time scales. Lightning is responsive to temperature on many time scales, but the sensitivity to temperature appears to diminish at the longer time scales. [Copyright &y& Elsevier]

Abstract: A vertical conduction current arises from the global ionospheric potential and the integrated electrical resistance between the Earth''s surface and the ionosphere. The conduction current density varies with the ionospheric potential and the vertical (columnar) resistance. At the surface, the conduction current density is known as the air–earth current. C.T.R. Wilson developed a measurement technique for the air–earth current in 1906, which was implemented by the British Meteorological Office at its Kew Observatory (51° 28′N, 0° 19′W) near London in 1909. Simultaneous measurements of air–earth current, potential gradient and positive air conductivity were made almost continuously until 1979 using the Wilson method on fine afternoons. A summary of the complete set of monthly mean measurements is presented here for the first time. The data span the nuclear weapons testing period and the UK Clean Air Act of 1956, both of which influenced the measurements obtained. Annual average values of the air earth current density at Kew are 0.97 pA·m−2 (1909–1931), 1.04 pA·m−2 (1932–1949) and 1.41 pA·m−2 (1967–1979). [Copyright &y& Elsevier]

The present study was aimed at analysing the main atmospheric dynamic mechanisms associated with the occurrence of intense rainfall events above the Huancayo observatory (12.05°S, 75.32°W, 3313 m asl) in the central Andes of Perú (Mantaro valley) from January 2018 to April 2019. To identify the rainfall events, we used a set of instruments from the laboratory of physics, microphysics and radiation (LAMAR) composed by in-situ pluviometric observations, satellite remote sensing data (GPM), Cloud Radar (MIRA-35c), Boundary Layer Tropospheric Radar (BLTR) and downscaling model simulations with WRF (resolutions: 18 km, 6 km and 2 km) and ARPS (0.5 km) models to analyse the dynamics of the atmosphere for the synoptic, meso and local processes that control the occurrence of these rainfall events. The results showed that all intense rainfall events are associated with the presence of thermal meso-scale circulations that transport moisture fluxes through passes with gentle slopes along both sides of the Andes. The easterly moisture fluxes come in from the South America Low Level Jet (SALLJ) and the westerly moisture fluxes from the Pacific Ocean. The arrival of these moisture flows to regions within the Mantaro valley depends on their coupling with the circulations at medium and high levels of the atmosphere. At the synoptic scale, the results show that the rainfall events can be separated into two groups: the first one associated with westerly circulations (WC) at the mid and upper levels of the atmosphere, generated by the weakening and eastern displacement of the anticyclonic Bolivian high-North east low (BH-NE) system, and the second associated with easterly circulations (EC) at the mid and upper levels of the atmosphere, generated by the intensification of the BH-NE system. The observed and simulated results showed that multicell convective systems of WC events are more extensive and deeper than EC events. This situation can be explained as the convergence of moisture fluxes from opposite directions occurred within the Mantaro basin for WC events. In contrast, for EC events, the convergence develops at the east Andes mountain range, following which the multicell storm system propagates westward, driven by easterly circulations. The EC events occur mostly in the summer months, while the WC events occur mostly in the autumn and spring months. Moreover, apparently the inertia gravity waves (IGWs) formed in the Amazon basin transport moisture and energy to the central Andes plateau and intensify the convection processes. • The study analyzes the main atmospheric dynamic conditions that generate intense rainfall events in the Peruvian central Andes. • All intense rainfall events are associated with thermal meso-scale circulations that transport moisture fluxes. • Easterly moisture fluxes coming from the South America Low Level Jet and the westerlies from the Pacific Ocean. • Rainfall events were separated into two groups: events with easterly circulations (EC) and with westerly circulations (WC) • The WC events were more extensive and deeper than EC events [ABSTRACT FROM AUTHOR]

This paper investigates the variability of monsoon clouds properties over the South African summer monsoon core zone (SAM: 20°-5°S; 12°-40°E) during the active and break spells of the monsoon seasons and compare the results to those Efon et al. (2016) observed over the West African summer monsoon (WAM) using CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellites merged data products. We first computed rainfall anomalies from the Tropical Rainfall Measuring Mission (dataset: TRMM-3B42) rainfall estimates for 1998–2016 to identify the active and break spells of the summer monsoon seasons. More break than active spells, especially in June occur over WAM, and over SAM, active spells are more common, especially in the month of January. Prolonged and successive rainfall can cause floods as observed in the 2010/2011 monsoon season over SAM. A comprehensive assessment is made of cloud properties during active and break spells. Both CBH and CTH exhibit trimodal distribution over SAM. Thicker clouds (with ΔH ≥ 3 km) occur more during the active than break spells. More cirrus cloud cells occur during the active spells (53%) than break spells (43%) over SAM and lesser deep convective clouds occur over SAM compared to WAM during the active spells. Mid-level clouds over SAM have more LWC and R liq compare to those occurring over WAM. High-level clouds over SAM are richer in IWC, INC and Rice in both monsoons spells than those over WAM. Deep clouds over SAM have larger R liq and R ice than those occurring over WAM. More atmospheric heating due to clouds in the active spells occur over WAM than SAM in the lower troposphere, and in the upper atmosphere, more heating of the atmosphere takes place SAM compare to WAM. This study has application in representing clouds better in regional weather and or climate models. • Journal title "African Summer Monsoon active and break spells cloud properties: Insight from CloudSat-CALIPSO". • Auhors: Efon Eric, Brice B. S. Wandjie, Lenouo Andre, Monkam David, and Manatsa Desmond. • Number of expected pages: 1 • Date of submission of revised version of the manuscript: 29 Dec. 2019. [ABSTRACT FROM AUTHOR]